The Design Of Synchronous White LED Driver In Current Mode PWM

White LED, as the best choice of back light of color LCD, has been widely applied to portable electronic fields, such as mobile phone, DC, MP3 and so on. In the recent years mobile phone has renewed continually and become more and more popular, and DC also become popular, all these impel output of white LED and its driver uprush. In order to satisfy requirements of different input voltage, different output current and different series number LED from the market, world famous semiconductor companies have developed all sorts of new pattern LED drivers. So design and research of white LED driver has become the hotspot of power supply market.This paper is mainly about research and design of white LED driver chip, and how to choose appropriate driving mode according to LED self-feature. Now mode of power management and controlling has converted from voltage control to current control, PWM current control adopts dual closed loop control, which improves system instant response rate and enhances system stability. Synchronous rectification technology adopts PMOS replacing schottky rectifying diode, which eliminates affects of diode dead voltage and improves work efficiency. The design of this paper adopts current PWM control mode and synchronous rectification technology and optimizes the performance of chip.This paper analyses working theory about driving chip of white LED and controlling mode circuit structure of current PWM; and designs main function modules of the chip in BiCMOS process, including bandgap circuit, oscillator circuit, error amplifier circuit,comparator circuit, synchronous rectification driving circuit, thermal shutdown circuit, etc; lists all the transistor-level circuit diagrams, all modules are simulated by Hspice EDA software and the simulating results are listed out as well.